Electrical frequency-changing apparatus of the thermionic type



ELECTRICAL FREQUENCY CHANGING APPARIVIJUS OF THE THERMIONIC TYPE Filed March 5, 1,926

m-gl l INVENTOR 1 Humfrgy' flndrewes A TTORNE Y Patented Oct. 20, 1931 UNITED STATES PATENT OFFICE EUMFBEY ANDREWES, 0F HIGHGATE, LONDON, ENGLAND, ASSIGNOR OF FIFTY PIER CENT TO RADIO PATENTS CORPORATION, OF N E'W' YORK,- N. Y., A CORPORATION OF NEW YORK ELECTRICAL FREQUENCY-CHANGING APPARATUS OF THE THERMIONIG TYPE Application filed March 5, 1926, Serial No. 92,433, and in Great Britain March 5, 1925 In the use of radio receiving and amplifying apparatus operating upon the wellknown method of transforming or changing the frequency of the received signal impulses into another and usually lower radio frequency before amplification and subsequent rectification of the lower radio frequency amplified impulses, certain difliculties are usually experienced. In this method of reception, known also as the supersonic amplification method, it is necessary to change the frequency of the incoming signals to a lower frequency suitable for operating the amplifier. This is customarily accomplished by providing a source of radio-frequency oscillationsor heterodyne-having a frequency approximating to that of the signals to be received and also some means for combining the said heterodyne oscillations with the incoming signals.

The object of the resent invention is to provide an improv apparatus and means for carrying out the frenquency changing operation particularly required for receivers of this type, without the disadvantages attendant upon the ordinary arrangement heretofore used.

In many cases usingthree electrode tubes with this type of receiver wherein the heterodyne or local oscillations are coupled into the circuits carrying the si difliculties are often foun in arriving at the proper coupling between the two, to ensure proper mixing of the two currents. This difliculty is overcome by the present invention.

Further in one of the arrangements forming the basis of this invention, it is possible to effect a reduction in the number of tubes as compared with the customary methods of frequency changing heretofore employed in con unction wit su usin three electr possibilities of radiating radio frequency energy from the receiving aerial are also reduced by theuse of this invention as com-' pared with previously lmown arrangements.

To carry this invention into effect I employ one or more four-electrode thermionic tubes preferably of the type having two grid al currents, some erheterodyne receivers e vacuum tubes. The

or control electrodes, one cathode and one anode.

Where two tubes are used one is employed to provide a local source of heterodyne oscillations, while the other is employed to provide a coupling or combining means between the local heterodyne oscillations and the incoming signals. To this end one of the grid electrodes of the latter tube is connected to the signal receiving and tuning circuit while the second grid electrode is connected to the local source of oscillation provided by the other four-electrode tube.

Two alternative forms of the invention are 1llustrated in the accompanying drawings, wherein:

Fig. 1 illustrates an arrangement employing two four-electrode tubes of the beforementioned type, wherein one such tube performs the functions of an oscillator, and the second tube acts as a combining and fro-- quency-changing tube.

Fig, 2 illustrates a simplified arrangement wherein a single tube only is employed which tube performs the dual function of oscillator and frequency changer.

In Fig. 1, V and V represent the two four-electrode tubes just referred to. One of these, namely V is provided with a circuit L 0 in which the local heterodyne oscillations are established by the action of the tube,

this circuit is joined between one of the grid electrodes, such as G and the ositive pole of the B battery B This battery is also connected to the anode of the tube. The two grid electrodes are connected together through the condenser G with a grid leak resistance R joined between the grid G and the negative pole of the filament lighting battery B The tube V provides the local heterodyne oscillations while thetube V provides the coupling means between these oscillations and the signal currents. These signal currents are established in the tuned circuit L G by connecting or coupling it to an aerial system in well-known manner as for example through the coupling coil L. Alternatively the point of this circuit whichis shown in the dia ram'as joined to the positive pole of the B battery, may be joined to any other point of zero or substantially zero radio frequency potential, such for example as one or other of the filament terminals of the valve. The tuned circuit L G is joined between one of the grid electrodes 2 of the tube V and the ositive pole of the B battery B The tube 1 then operates as a detector tube by virtue of the grid condenser C and the resistance R, so that the amplified signal impulses would normally be repeated in the anode circuit of the said tube this circuit being completed through the.B battery B The second grid electrode 3 of this tube is joined in parallel with one of the grid electrodes 2 of the second tube V so that the potential changes occurring on this gridelectrode 2 are thereby communicated to the grid 3 of the first tube V By this means the plate or anode current flowing through the valve V will be modulated both by the signal impulses communicated to the grid 2 and by the local heterodyne impulses communicated to the grid 3. The results will be the production in the anode circuit of this tube of so called beat or heterodyne currents having a frequency equal to the difference between the frequencies of the two said sources of modulation. This beat frequenc is thereby communicated to the circuit L 3 included in the anode circuit of this tube, and tuned to this beat frequency, from which it is transmitted by the coupling L L to the intermediate frequency or long-wave amplifier of any standard and well known type as is commonly done in all previously knownreceivers of the supersonic type.

The apparatus arranged as shown thus constitutes a complete frequency-changing unit, as its function is to change the frequency of any currents supplied to it through the input coil L, and to deliver lower frequency currents from its output coil L The said output currents although of lower frequency have impressed upon them any modulation characteristics which may be impressed upon the higher frequency input currents, the fundamental or carrier radio frequency only being changed without affecting any lower audio frequency components or modulation of the input currents.

The two tuning condensers C and C may be mechanically coupled together to work 111 unison from a single control knob or handle, provided that the necessary frequency difference is maintained between the natural frequencies of the two circuitsL C and L G this difference being equal to or sensibly equal to the frequency of the output currents delivered from the coil L4. Provided that the coils L L are similar in electrical constants the desired results can be obtained when the two condensers C and C have elecv trical characteristics of the straight-line frequency typethat is to say such that the electrical capacity of each of these condensers varies in such a manner that equal divisions of movement of the condensers produce equal frequency changes in the two circuits. The two condensers are then directly coupled together with a slight displacement between them to give the necessary frequency difference. This frequency difference will then be maintained at all points on the scale of the condensers provided that they have the above mentioned electrical characteristics.

Alternatively two condensers of normal straight-line capacity or linear type may be coupled together and two dissimilar coils be used for L and L to give the desired frequency difference. This is indicated in the diagram by dotted lines joining condensers C and C Furthermore, in the circuit L 0 and L C the variable condensers may be substituted by fixed condensers, in which case the inductances L L would be continuously variable and might take the form of variometers. The moveable elements of the two coils or variometers whereby the inductance value is varied may also be mechanically coupled together to work in unison from a single control knob or handle, provided that the necessary frequency dilference is maintained between the natural frequencies of the two circuits LlC and L C It should be understood that the method of coupling the local heterodyne oscillations to the incoming signal current as herein de scribed is not limited to the use of the precise arrangement of the second tube V set out in the diagram, but may be adaptedto any of the previously well known methods of producing heterodyne oscillations. The connections to the two grid electrodes 2 and 3 may likewise be interchanged without departing from the spirit of the invention.

Alternatively, the separate functions of the two four-electrode tubes herein described may be performed in a single tube, as illustrated in Fig. 2. In this arrangement, as in the two-tube method, signals'currents are established in the circuit L G, by coupling to the input circuit L. The tube V then operates as a detector tube by virtue of the grid condenser C and the grid leak R the circuit L G being connected across the grid Gr" and the filament of the tube V Local heterodyne oscillations are provided by causing the tube V to oscillate by connecting the inner grid Gr to a second circuit L C This circuit is connected between the grid G, and the anode of the tube. Potential changes of the grid G' will therefore cause corresponding changes in the electron sti eam controlled by the grid G",, on which is impressed the incoming signal and hence the so called beat or heterodyne currents will be produced in the anode circuit of the tube. As in the case of the corresponding frequency-changing tube shown in Fig. 1, a third tuned circuit v at a positive potential with respect to the other, a grid leak resistance, an oscillatory circuit in which oscillations of the frequency of and due to the received signals are established, one of the grid electrodes'being connected therewith, a local source of oscillations of difierent frequency, said second grid being subject to potential fluctuations therefrom and connected throu h said grid leak resistance to the cathode 0 the tube, an oscillatory circuit tuned to the resultant or beat frequency, and an anode connected to said last mentioned oscillatory circuit. 7

2. Frequency-changing apparatus of the thermionic type, com rising in combination a four-electrode tu e having a heated cathode, an anode and a plurality of control electrodes, means including one of said control electrodes for generating oscillations, a second source of oscillations, means including the other control electrode for combining said generated oscillation with said second oscillations to produce a beat note, an output circuit including the anode of the said tube tuned to the beat frequency resulting from the combination of the two frequencies impressed upon the control electrodes and means for maintaining one of said control electrodes positive with respect to the other.

3. Frequency-changing apparatus of the thermionic type, comprising a four-electrode tube having a heated cathode, an anode and a plurality of control electrodes, an oscillatory circuit in which signals are received one of the control electrodes of saidtube being connected with said oscillatory circuit, a local source of oscillations of different frequency from that of the si al oscillations,

a second control electrode su jected to potential fluctuations from said local source'of oscillations, means for maintaining said second electrode positive with respect to said first I control electrode, and an oscillatory circuit tuned .to the resultant or beat frequency of said local and received oscillatory currents said anode connected with said last mentioned oscillatory circuit tuned to sultant or beat frequency.

I 4. Frequency-changing apparatus of the thermiomc type comprising a four-electrode tube having a heated cathode, an anode and a plurality of grid electrodes, an. oscillatory circuit tuned to the incoming -si 'al frequency connected to one of said gri a local the resource of oscillations of different frequency from that of the signal frequency, means for communicating potential fluctuations of the local fre uency from the said source to a second grid of the thermionic tube, means for maintaining said second grid at a high posi-;

tive potential with respect to said first grid and an oscillatory circuit in the anode circuit of the said tube tuned to the resultant or beat frequency.

5. Frequency-changing apparatus of the thermionic type, comprising a four-electrode tube comprising a first and secondgrid and a cathode, a source of incomin signals of a predetermined frequency, a circuit tuned toa frequency differing from the frequency of the incoming signals, one of said grid electrodes'being connected to the source of incoming signals, the second of said grid electrodes being connected to said last mentioned tuned circuit and means for maintaining said second grid at a positive potential with respect to the first mentioned grid electrode and to the cathode of the tube.

6. In a radio circuit, a vacuum tube comprising) two grids and a cathode, one of said grids eing adjacent said cathode and the second of said grids more remote therefrom,

said tube is given a negative characteristic 1 for maintaining oscillations in the said circuit connected with the inner grid electrode.

7. In a radio circuit, a four-electrode tube containing aheated cathode, an anode'and two grid electrodes, a circuit connected to one grid electrode for receiving the incoming sig nal, a local source having a frequency differing by a desired amount from that of the incoming signals, a second oscillatory circuit connected to the second grid electrode and to said localsource, a third oscillatory circuit connected in series with the anode of the said tube, and tuned to the beat frequency resulting from the intersection of the currents in the first mentioned circuits and means for maintaining the second grid positive with respect to said first grid.

8. Frequency-changing apparatus of the thermionic type comprising a four-electrode tube having a heated cathode, an anode and two grid electrodes, an oscillatory circuit, means for generating oscillations of the frequency of and due to the received signals in said oscillatory circuit, one of said grid electrodes being connected to said oscillatory circuit, means including a. second four-electrode thermionic tube having a heated cathode and anode and two grids capacitatively coupled for generating oscillations of difierent frequency from said first mentioned oscillatlon, said second grid of said first tube being subject to potential fluctuations of said last mentioncd means, and means for maintaining one of said grids of said second tube at a positive potential with respect to the other grid, an oscillatory circuit tuned to the resultant or beat frequency and connected to said anode of said second tube, one of said grids of said second tube being connected in said local source of oscillation and also with said secong. grid of the first mentioned thermionic tu e.

9. Frequency-changing apparatus of the.

thermionic type having in combination a four-electrode tube comprising an anode, a cathode and a first and second grid, said first grid being adjacent said cathode and the second grid more remote therefrom, a circuit tuned to the frequency of received signals and said second grid being connected thereto, a second circuit tuned to a frequency differing from the frequency of the incoming signals, said first grid electrode situated nearest to the cathode of the tube being connected to said second tuned circuit, means for maintaining said first grid at a positive potential with respect to the second grid electrode and to the cathode of the tube whereby said tube is given a negative characteristic for the purpose of maintaining oscillations in the said circuit connected with the inner grid electrode, and an anode circuit connected to said anode tuned to the beat frequency resulting from the combination of the two frequencies impressed upon the grid electrodes.

In testimony whereof I have signed my name to this specification.

HUMFREY ANDREWES. 

